The present invention relates to techniques for controlling transmission over a radio channel between a sending unit and a group of receiving units. It is in particular directed to third-generation wireless networks.
In the present description, the invention will be described more particularly in its application, non limiting, to third generation radio communication networks of the UMTS type (“Universal Mobile Telecommunication System”). In this system, the invention finds application within the framework of the High Speed Uplink Packet Access (HSUPA) feature currently being specified by the 3GPP (3rd Generation Partnership Project)—also named “FDD enhanced uplink” in 3GPP terminology, or “E-DCH” according to the transport channel's name. This feature is described particularly in the technical specification TS 25.309, V0.2.0, “FDD Enhanced Uplink; Overall description; Stage 2 (Release 6)”, published in June 2004 by the 3GPP.
FIG. 1 shows the architecture of such a UMTS network. The switches of the mobile service 10, belonging to a core network (CN), are linked on the one hand to one or more fixed networks 11 and on the other hand, by means of a so-called lu interface, to command equipment 12 or RNCs (“Radio Network Controllers”). Each RNC 12 is linked to one or more base stations 13 by means of a so-called lub interface. The base stations 13, distributed over the territory covered by the network, are capable of communicating by radio with the mobile terminals 14, 14a, 14b called UE (“User Equipment”). The base stations can be furthermore communicate with one another by means of a so-called lur interface. The RNCs and the base stations form an access network called UTRAN (“UMTS Terrestrial Radio Access Network”).
The UTRAN comprises elements of Layers 1 and 2 of the ISO model with a view to providing the links required on the radio interface (called Uu), and a stage 15A for controlling the radio resources (RRC, “Radio Resource Control”) belonging to Layer 3, as is described in the 3GPP TS 25.301 technical specification “Radio Interface Protocol Architecture”, version 6.0.0 published in December 2003 by the 3GPP. In view of the higher layers, the UTRAN acts simply as a relay between the UE and the CN.
FIG. 2 shows the RRC stages 15A, 15B and the stages of the lower layers which belong to the UTRAN and to a UE. On each side, Layer 2 is subdivided into a radio link control (RLC) stage 16A, 16B and a medium access control (MAC) stage 17A, 17B. Layer 1 comprises a coding and multiplexing stage 18A, 18B. A radio stage 19A, 19B caters for the transmission of the radio signals from trains of symbols provided by the stage 18A, 18B, and the reception of the signals in the other direction.
There are various ways of adapting the architecture of protocols according to FIG. 2 to the hardware architecture of the UTRAN according to FIG. 1 and in general various organizations can be adopted depending on the types of channels (see section 11.2 of the 3G TS 25.401 technical specification “UTRAN Overall Description”, version 6.3.0 published in June 2004 by the 3GPP). The RRC, RLC and MAC stages are typically located in the RNC 12. When several RNCs are involved, the MAC sublayer can be apportioned among these RNCs, with appropriate protocols for the exchanges on the lur interface, for example ATM (“Asynchronous Transfer Mode”) and AAL2 (“ATM Adaptation Layer No. 2”). These same protocols may also be employed on the lub interface for the exchanges between the MAC sublayer and Layer 1.
The RLC sublayer is described in the 3G TS 25.322 technical specification “RLC Protocol Specification”, version 6.1.0 published in June 2004 by the 3GPP. In the send direction, the RLC stage 16A, 16B receives, according to the respective logical channels, data streams consisting of service data units (RLC-SDU) arising from Layer 3. An RLC module of the stage 16A, 16B is associated with each logical channel so as in particular to perform a segmentation of the RLC-SDU units of the stream into blocks, or protocol data units (PDU, “Packet Data Units”) addressed to the MAC sublayer and comprising an RLC header. In the receive direction, an RLC module conversely performs a reassembling of the RLC-SDU units of the logical channel from the blocks received from the MAC sublayer.
The MAC sublayer is described in the 3G TS 25.321 technical specification “MAC Protocol Specification”, version 6.2.0 published in June 2004 by the 3GPP. It transposes one or more logical channels onto one or more transport channels.
The infrastructure of a cellular network typically comprises base stations distributed over the covered territory for communicating with mobile stations located in the zones, or cells, that they serve. The macrodiversity technique consists in providing for a mobile station to be able to communicate simultaneously with separate base stations in such a way that, in the downlink direction (from the base stations to the mobile stations), the mobile stations receive the same information several times and, in the uplink direction, the signal transmitted by the mobile station is picked up by the base stations in order to form different estimates that can then be combined in the network infrastructure.
Macrodiversity procures increased reception that improves the performance of the system due to the combination of different observations of a same information item. It also makes it possible to carry out soft intercellular transfers (“soft handoff”, SHO) when the mobile station is moving. Macrodiversity techniques are provided in the UMTS system, in the context of wide band CDMA (W-CDMA) for frequency duplex communications (FDD). For example, the fact that a radio signal value transmitted for example by a UE is received by several Node-Bs is referred to as macrodiversity on the uplink, and such macrodiversity results from the reception of an estimate of radio signal transmitted from the UE, through a so-called active set of Node-Bs.
UMTS proposes a “High Speed Downlink Packet Access” (HSDPA) feature, an overall description of which may be found in the 3GPP 25.308 technical specification “UTRA High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2”, version 6.1.0 published in May 2004 by the 3GPP. HSDPA allows high rate downlink transmission, i.e. from a base station to a mobile station, of data to a set of UEs located in the coverage area of the base station. This service is based on a high speed downlink shared transport channel, named HS-DSCH (“High Speed—Downlink Shared Channel”). In the FDD mode, this channel has the following characteristics in particular: (i) a transmission time interval (TTI) of 2 milliseconds corresponding to 3 timeslots of 666 μs; (ii) hybrid processes for requesting data retransmission of the HARQ type (“Hybrid Automatic Repeat reQuest”); and (iii) an adaptive coding and modulation mechanism.
In the access network, part of the MAC layer, the MAC-hs, is located in Node-Bs, so that a higher throughput can be achieved. This architecture is illustrated in FIG. 3, and described in the 3GPP TS 25.401 technical specification “UTRAN overall description”, version 6.3.0, release 6, published in July 2004 by the 3GPP.
The above mentioned new “High Speed Uplink Packet Access” (HSUPA) feature, also called “FDD enhanced uplink”, is currently being specified by the 3GPP, in order to provide high speed uplink transmission, i.e. from a UE to the access network. This service is based on the so-called “E-DCH”, a new type of transport channel which supports HARQ, adaptive modulation and coding, and Node-B scheduling of the uplink data transmissions. At the MAC level, a new MAC termination point, the MAC-e, has been introduced in the UTRAN architecture, and more specifically at the Node-B level. This architecture is illustrated in FIG. 4, and described in the 3GPP TS 25.309 draft specification “Enhanced uplink UTRA FDD; Stage 2”, version 0.2.0, published in July 2004 by the 3GPP.
It has been agreed in 3GPP that such a transport channel would support uplink macrodiversity i.e. selection combining. This means that, in a soft handover (SHO) situation, the MAC-e protocol entity in the UE can have multiple peer MAC-e entities in the network i.e. one per Node-B in the active set. It should be noted that there can be only one MAC-e per Node-B, since each Node-B combines the uplink radio links it has with a UE at the physical layer.
The principle is that a PDU submitted to MAC-e in the UE shall be delivered successfully to at least one of a set of Node-Bs. These Node-Bs can then forward the received PDU to the serving RNC. The RNC performs selection combining in the case where several Node-Bs have received the same PDU correctly. The HARQ protocol is designed such that each Node-B independently acknowledges received MAC-e PDUs. The UE may consider a PDU transfer successful if at least one of the set of Node-Bs to which a MAC-e PDU was sent has positively acknowledged the PDU.
In certain situations, it may be beneficial to be more selective than such a transmission scheme to at least one of the Node-Bs. Indeed, in such a scheme, there is no control as to which Node-B effectively receives and acknowledges a PDU. The current HARQ protocol scheme considers that a PDU transmission is complete as soon as at least one Node-B of a set of Node-Bs, regardless of which one in the set, has positively acknowledged the transmitted PDU. However, the transmitted PDU may have been more specifically intended to another particular Node-B of the set of Node-Bs. Therefore, there is no guarantee that said particular Node-B has correctly received the transmitted PDU.
More generally, when using a shared radio channel a sending unit can generally not be sure that a particular receiving unit or a subgroup of receiving units from a group of receiving units has correctly received transmitted information.
The purpose of the invention is to provide an improved scheme. In particular, it is one object of the invention to provide a more selective scheme. Embodiments and benefits of the invention will be detailed afterwards.